In daily life, the combined gas law is used for refrigeration and maintaining the proper air pressure in car tires. The combined gas law also helps scuba divers adapt to their underwater environments.
The combined gas law applies when there is a closed container or compartment with a fixed amount of gas. The combined gas law is so named because it is a combination of three other laws, which are Gay-Lussac's gas law, Charles' law and Boyle's law. Collectively, these laws explain that the ratio of an element with pressure and volume to temperature remains fixed for a given amount of gas.
One example of the combined gas law applies to scuba diving. In scuba divers, human lungs are the container that hold the gas. The pressure in water is greater than pressure in air, and water pressure increases with depth. With each additional foot that divers descend, water pressure rises. Therefore, divers must make adjustments to maintain the proper pressure balance between their lungs and the water. This change must also take place gradually to create an equilibrium. If a diver with full lungs ascends rapidly on a warm day, the volume of air in the lungs can expand quickly. Therefore, he or she must exhale quickly to allow gas in the lungs to escape.
Another instance of the combined gas law applying to daily life is refrigeration. Refrigerators apply the combined gas law when they remove heat from their systems. The process of refrigeration starts when the compressed gas stored in refrigerator coils expands. This in turn lowers the temperature of the gas and transfers heat energy from the coil material to the gas. As gas is pumped through the coils, its pressure compresses the heat energy. This raises the temperature of the gas. Heat is released through the coils into the outside air, which in turn allows the refrigerator to stay cool. The cycle repeats when compressed gas is pumped through the system again.
Maintaining proper pressure in car tires is another application of the combined gas law. As cars proceed down the road, the amount of gas in their tires remains constant. However, the temperature of the air within the tires increases. Because tires have some amount of elasticity, the volume in the tires also increases. Since tires vary in size and composition, tire manufacturers recommend a proper level of air pressure for tires, which varies based on the type of tire. Although the recommended pressure numbers change, all tires have a minimum and maximum recommendation for pounds per square inch, or PSI. Drivers maintain the proper amount of pressure in their tires by keeping them inflated above the minimum PSI but below the maximum PSI. For most tires, maximum pressure is somewhere between 30 and 32 PSI. While some drivers are tempted to fill their tires to the maximum level, doing so can be hazardous, and it can shorten the lifespan of the tires. When tires are inflated to the maximum, it creates a change in handling. Tires that are inflated to the maximum amount have less give on the sidewall. While this enables fast cornering, it can reduce the car's ability to brake efficiently, which in turn leads to sliding. Tires that are inflated to the maximum amount cause the center of the tire to wear out and reduce traction, which can be unsafe for drivers.